Exemplary embodiments of the present invention relate to the art of turbomachines and, more particularly, to a turbine bucket for a turbomachine.
In gas turbines, an axial gap exists between a trailing edge of an upstream nozzle side wall, and a leading edge of a downstream bucket platform. Hot gases exit upstream nozzle passages and pass over the axial gap before entering bucket row passages. A portion of the hot gases becomes stagnate at leading edge portions of the bucket platform. The stagnate flow or bow wave generates a circumferential pressure gradient at the axial gap. The circumferential pressure gradient generated by the bow wave drives hot gases to the axial gap and into a trench cavity area and may even reach a wheel space cavity area. The hot gases mix with cool purge flow passing through a wheel space portion of the turbine, travel circumferentially, and exit the trench cavity at a circumferential low pressure region. Hot gases reaching lower portions of the wheel space may cause damage and lower an overall operational life of the turbine. Increasing the cool purge flow to combat the detrimental effects of the hot gases lowers turbine efficiency.